Global warming: Global warming refers to the phenomenon of sustained increase in global temperature due to environmental pollution and deforestation. It is caused by the emission of Green House Gases that include, particularly, carbon dioxide. The increase in the level of carbon dioxide raises the temperature of the earth surface. This risen temperature accelerates the melting of polar ice that further leads to the rise in the sea level. Thus, the incidence of natural calamities rises due to disturbed ecological balance, thereby, posing a threat to human life.